1. Field of the Invention
The present invention relates to a beam irradiation apparatus and a beam irradiation method. Moreover, the present invention relates to a method for manufacturing a thin film transistor using the apparatus and the method.
2. Description of Related Art
A research has been conducted concerning a thin film transistor having a channel-forming region in a poly-crystalline semiconductor film (hereinafter this thin film transistor is referred to as poly-crystalline TFT) as a semiconductor element in a display device, an integrated circuit, or the like. With the development of the display device and the integrated circuit, further enhancement of the characteristic of the poly-crystalline TFT has been expected.
Consequently, in order to enhance the characteristic of the poly-crystalline TFT, crystallization of the semiconductor film by a continuous wave laser irradiation apparatus has been examined. For example, there is a method for crystallizing an a-Si film in such a way that the a-Si film is patterned into linear or island-shape over a glass substrate, and then an energy beam output continuously to time from the continuous wave laser irradiation apparatus is irradiated and scanned thereto (Refer to patent document 1). The patent document 1 describes that when the semiconductor thin film is patterned into linear or island-shape in advance, the crack and the like can be prevented because the temperature of the glass substrate does not increase. The patent document 1 also describes in FIG. 29 and FIG. 31 that a blocking plate with an opening provided is used to crystallize only the necessary part of the a-Si film selectively without giving damage to the glass substrate and without peeling the a-Si film.
Moreover, a galvanometer mirror (refer to patent document 2) or a polygon mirror (refer to patent document 3) is used as means for scanning (also referred to as deflecting) the laser light (also referred to as a laser beam). Since the galvanometer mirror and the polygon mirror can easily increase the scanning speed, the burden on the irradiation apparatus can be reduced.    Patent Document 1
Japanese Patent Unexamined Publication No. 2003-86505 bulletin    Patent Document 2
Japanese Patent Unexamined Publication No. 2003-86507 bulletin    Patent Document 3
Japanese Patent Unexamined Publication No. 2003-45890 bulletin